Demands of services using wireless communication are rapidly increasing, but frequency bands having good transmission characteristics and which are easy in terms of component development are already occupied. Thus, cognitive radio technology is used for a secondary user who desires to provide a new service using unused frequency channels found by temporally and spatially checking frequency channels that are licensed and allowed to a primary user. The primary user and the secondary user are communication systems operated by different services or operators and are described below.
The present invention corresponds to technology, which is being standardized by IEEE 802.22, and in more detail, functional requirements are being determined in order to create a standardization draft.
According to the IEEE 802.22 standardization, it is desired that a wireless Internet service is provided using time and space unused by the primary user of TV or wireless devices using a TV frequency band or a frequency band currently used for wireless microphone communication (e.g., a frequency band from 54 MHz to 698 MHz corresponding to TV channel numbers 2 to 51 in the United States, or a frequency band from 41 MHz to 910 MHz internationally). In order for an IEEE 802.22 system (a Base Station (BS), a Customer Premises Equipment (CPE), and a core network) to use the assigned TV frequency band, the BS of the secondary user and the CPE, which is a terminal of the secondary user, must know a current state of the frequency channels. To do this, the BS and the terminal of the secondary user always monitor a channel usage state by scanning the current TV frequency channels, i.e., the frequency band from 41 MHz to 910 MHz. Therefore, when the primary user desires to use a frequency channel being used by the secondary user, the secondary user can quickly hand over the frequency channel to the primary user.
As described above, the present invention is related to a method of sensing and managing frequency channels when 6, 7, or 8 MHz is set as a single frequency channel from the frequency band from 41 MHz to 910 MHz assigned to TV broadcasting in a multiple Frequency Assignment (FA) system, i.e., an IEEE 802.22 standard system, and is similar to Dynamic Frequency Selection (DFS) technology suggested by IEEE 802.16.
The DFS technology suggested by IEEE 802.16 is a technology of scanning for a wireless data communication service in an unlicensed bandwidth to determine whether frequency channels of a primary user are used, assigning a frequency channel unused by the primary user to the wireless data communication service, releasing the frequency channel from the wireless data communication service by using a BS according to a request of the primary user, and assigning a new channel to the wireless data communication service.
In this point of view, a technology field related to spectrum sensing in a multiple FA system according to an embodiment of the present invention is almost the same as the field of spectrum sensing technology of IEEE 802.22 and the DFS technology of IEEE 802.16.
However, in the conventional DFS technology of IEEE 802.16, in order to provide a wireless Internet service in an unlicensed bandwidth, a method used by a BS for requesting a terminal for measurement of a state of a selected frequency channel and receiving a measured result is used. In the conventional method, the BS only passively acquires information regarding the state of frequency channels licensed to a primary user, and thus, communication quality degradation and communication impediment of the primary user may occur due to a decrease in the reliability of the spectrum sensing in a process of assigning or changing a frequency channel to a new secondary user using the passively acquired state information, and data transmission efficiency may decrease due to an increase of an overhead signal such as a frequency channel state sensing request message.
Thus, in order to assign frequency channels licensed to a primary user to a new secondary user without affecting communication quality of the primary user, a BS of the secondary user must always maintain optimum information on the state of the frequency channels licensed to the primary user.
In order to do this, terminals and the BS of the secondary user must actively determine the state of the frequency channels licensed to the primary user using the spectrum sensing. In addition, for the spectrum sensing, instead of a simple periodic sensing method, an efficient method of changing a sensing period in consideration of whether the primary user uses the frequency channels is required.